Node.js JWT authentication errors: “Invalid Signature”, “Token Expired”, or malformed token

I’m implementing JWT-based authentication with Node.js (using jsonwebtoken). I frequently encounter errors such as: • JsonWebTokenError: invalid signature • TokenExpiredError: jwt expired • JsonWebTokenError: jwt malformed / invalid token What typically causes these JWT errors, and how do I resolve them correctly?

JWT issues in Node.js often stem from incorrect signing/secrets, malformed headers, or improper expiration logic. Here's how to address them:

🔍 Common Causes & Solutions Error Message Root Cause Fix invalid signature Mismatch between secret used to sign and verify tokens, or encoded differently (e.g. including quotes or base64) Ensure process.env.JWT_SECRET is identical in both jwt.sign() and jwt.verify() without quotes or unintended encoding GUVI+1GitHub+1InfiniteJS+2Stack Overflow+2GitHub+2Stack Overflow+2GitHub+2Stack Overflow+2Stack Overflow

jwt expired Token expiration time (exp) has passed or refresh logic missing Send proper error response, implement refresh tokens for seamless re-authentication GUVIcontextneutral.com

jwt malformed / invalid token Token extracted incorrectly (e.g., includes 'Bearer ' prefix or JSON string quoting); or characters altered in transit Remove prefix and extra quotes, e.g. Authorization: Bearer and split before verify Stack OverflowStack Overflow

🛠️ Key Fixes

1. Verify token extraction correctly js CopyEdit const authHeader = req.headers.authorization; const token = authHeader?.split(' ')[1]; // remove "Bearer" Do not wrap secrets in quotes or alter JWT content before verifying InfiniteJS+15Stack Overflow+15Stack Overflow+15Stack Overflow
2. Match signing secret and algorithm consistently js CopyEdit const token = jwt.sign(payload, process.env.JWT_SECRET, { algorithm: 'HS256', expiresIn: '1h' }); jwt.verify(token, process.env.JWT_SECRET, (err, decoded) => { ... }); Make sure both use the same HS256 (or chosen) algorithm CodingTechRoom+1GeeksforGeeks+1
3. Handle expired tokens gracefully js CopyEdit jwt.verify(token, secret, (err, decoded) => { if (err && err.name === 'TokenExpiredError') { return res.status(401).send({ message: 'Token expired, login again' }); } // ... }); Use refresh tokens to renew sessions without forcing re-login Codez Up+5GUVI+5contextneutral.com+5InfiniteJS

🧩 Practical Example js CopyEdit // Generating token const token = jwt.sign({ userId: user._id }, process.env.JWT_SECRET, { expiresIn: '1h', algorithm: 'HS256' });

// Verifying middleware function verifyToken(req, res, next) { const auth = req.headers.authorization; const token = auth && auth.split(' ')[1]; if (!token) return res.status(401).send({ message: 'Missing token' });

jwt.verify(token, process.env.JWT_SECRET, (err, decoded) => { if (err) { if (err.name === 'TokenExpiredError') { return res.status(403).send({ message: 'Token expired' }); } return res.status(401).send({ message: 'Invalid token' }); } req.user = decoded; next(); }); }

👀 TL;DR • Invalid signature = secret mismatch or wrong encoding • Expired token = needs refresh or user re-login • Malformed token = wrong extraction (e.g. quotes, Bearer prefix) Ensure secrets match, tokens are extracted cleanly, and errors are handled with recovery logic.

🧷 Tags for Posting nodejs, jsonwebtoken, jwt, authentication, security, token-expiration, error-handling